Use absolute RPATHs while linking due to a binutils bug

Use -rpath-link with the absolute paths to the respective build dirs
to work around a binutils bug that causes $ORIGIN to not be used while
linking.

Includes a unit test that manually checks the RPATH value written out
to ensure that it uses $ORIGIN.

See: https://sourceware.org/bugzilla/show_bug.cgi?id=16936

Closes https://github.com/mesonbuild/meson/issues/1897

mesonbuild/compilers.py

@@ -337,7 +337,12 @@ def build_unix_rpath_args(build_dir, from_dir, rpath_paths, install_rpath):
                 paths = padding
             else:
                 paths = paths + ':' + padding
-        return ['-Wl,-rpath,' + paths]
+        # Rpaths to use while linking must be absolute. These are not used
+        # while running and are not written to the binary.
+        # https://github.com/mesonbuild/meson/issues/1897
+        # https://sourceware.org/bugzilla/show_bug.cgi?id=16936
+        linkpaths = ':'.join([os.path.join(build_dir, p) for p in rpath_paths])
+        return ['-Wl,-rpath,' + paths, '-Wl,-rpath-link,' + linkpaths]
 
 class CrossNoRunException(MesonException):
     pass

run_unittests.py

@@ -49,6 +49,9 @@ def get_dynamic_section_entry(fname, entry):
 def get_soname(fname):
     return get_dynamic_section_entry(fname, 'soname')
 
+def get_rpath(fname):
+    return get_dynamic_section_entry(fname, 'rpath')
+
 
 class InternalTests(unittest.TestCase):
 
@@ -1133,6 +1136,25 @@ int main(int argc, char **argv) {
             self.assertTrue(os.path.exists(distfile))
             self.assertTrue(os.path.exists(checksumfile))
 
+    def test_rpath_uses_ORIGIN(self):
+        '''
+        Test that built targets use $ORIGIN in rpath, which ensures that they
+        are relocatable and ensures that builds are reproducible since the
+        build directory won't get embedded into the built binaries.
+        '''
+        if is_windows() or is_cygwin():
+            raise unittest.SkipTest('Windows PE/COFF binaries do not use RPATH')
+        testdir = os.path.join(self.common_test_dir, '46 library chain')
+        self.init(testdir)
+        self.build()
+        for each in ('prog', 'subdir/liblib1.so', 'subdir/subdir2/liblib2.so',
+                     'subdir/subdir3/liblib3.so'):
+            rpath = get_rpath(os.path.join(self.builddir, each))
+            self.assertTrue(rpath)
+            for path in rpath.split(':'):
+                self.assertTrue(path.startswith('$ORIGIN'), msg=(each, path))
+
+
 class WindowsTests(BasePlatformTests):
     '''
     Tests that should run on Cygwin, MinGW, and MSVC